Biochemical and immunological studies indicate that the GABAA receptor contains at least two types of subunit. Here we report that coexpression of two GABAA receptor subunit clones (alpha and beta) in Xenopus oocytes yields receptors with many biophysical properties of native GABAA receptors. These include ion selectivity, multiple single-channel conductance states, voltage-dependent gating and rectification, and complex desensitization kinetics. Furthermore, the receptors are competitively inhibited by bicuculline and display the expected allosteric and agonist effects of the barbiturate pentobarbital. The expressed receptors, however, appear to be activated by one molecule of GABA instead of two and fail to show potentiation by benzodiazepines. This implies that an additional factor(s) or subunit(s) is required for the reconstitution of a fully functional GABAA receptor.